Phantom

ABSTRACT

This invention provides an ultrasonic phantom that can respond to different ultrasonic intensities. Such ultrasonic phantom comprises a gel comprising a low-boiling compound in the form of droplets sealed therein. The invention also provides an assay technique using such phantom. This invention enables regulation of components of droplets, droplet size, and the ultrasonic intensity at which droplets are vaporized upon mixing of droplets with different sizes. This enables visualization of whether or not ultrasound beams that exceed relevant different ultrasonic intensities have been applied.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP2006-171744 filed on Jun. 21, 2006, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a phantom that indicates a dose ofultrasound beams radiated from an ultrasonic device used formeasurement, diagnosis, medical treatment, or other purposes.

2. Prior Art

In recent years, great importance tends to be attached to the quality oflife of a patient after medical treatment for a disease. In the case ofserious diseases such as cancer, the social demand for minimallyinvasive therapeutic methods is also increasing. At present, endoscopicoperations or laparoscopic operations that involve insertion of atubular guide into the body or radio-wave cautery that involvesinsertion of a needle-like therapeutic instrument into the body aremainly employed as minimally invasive treatment techniques in clinicalpractice, although such techniques involve invasion of the body with aninstrument. In contrast, ultrasound beams can converge in an area of 1cm×1 cm or smaller in the body from the outside of the body withoutinsertion of an instrument into the body, based on the relation betweenwavelength and attenuation inside body. With the utilization of suchproperties, clinical application of minimally invasive ultrasonictherapy has begun. At present, the most clinically advanced ultrasonictherapeutic technique is the high-intensity focused ultrasound (HIFU)therapy, which is targeted at treating hysteromyoma and breastcarcinoma. This therapeutic technique involves irradiation of anaffected area with high-intensity focused ultrasound (HIFU) to raise thetemperature at the affected area to a protein aggregation temperature orhigher within several seconds, thereby cauterizing the tissue at theaffected area. In addition to HIFU therapy, the following ultrasonictherapeutic techniques are available; for example, sonodynamic therapythat involves cauterization of a target such as a tumor using activeoxygen resulting from a phenomenon referred to as acoustic cavitationwith the utilization of the interaction between a sensitizer and aultrasonic beam and ultrasound-accelerated drug therapy, which isintended to accelerate drug efficacy by improving the ability of a drugto permeate an affected area with the use of ultrasound beams incombination with an existing drug.

In these therapeutic techniques involving the use of ultrasound beams,an ultrasonic generator is not brought into contact with the area to betreated. This requires monitoring of the area of treatment via adiagnostic imaging apparatus or the like. In addition to monitoring, itis important that a treatment plan be designed in advance so as to applyan adequate dose of ultrasound beams to the area of treatment and so asto prevent an inadequately large dose of ultrasound beams fromirradiating areas other than the area of treatment, in order to moreaccurately perform selective treatment.

A treatment plan refers to predetermination of an area that is to beirradiated with ultrasound beams. In order to confirm the effectivenessof the plan and whether or not the apparatus would function as planed,it is required to prepare an ultrasonic phantom that can mimic a livingorganism and that is constructed to indicate the degree of ultrasonicirradiation. It is also necessary to irradiate the ultrasonic phantomwith ultrasound beams to confirm the conditions of ultrasonicirradiation with the use of the ultrasonic phantom, prior to theapplication of the treatment plan to a human body.

Up to the present, an ultrasonic phantom that allows visualization ofsecondary actions resulting from ultrasonic application instead ofultrasonic energy has been devised as ultrasonic phantom as mentionedabove. An example thereof is an ultrasonic phantom that uses a solubleprotein as an indicator to detect temperature increase resulting fromultrasonic irradiation (C. Lafon et al., Proc., IEEE UltrasonicsSymposium, pp. 1295-1298, 2001). This utilizes the phenomenon whereby aprotein is solidified and aggregated upon thermal denaturation, whichincreases the light scattering intensity compared with that beforedenaturation. Also, with the utilization of the phenomenon whereby asubstance having a higher oxidizing power, such as a hydroxyl radical,is generated as a result of acoustic cavitation upon ultrasonicirradiation, a reaction substrate that develops color upon oxidation maybe used as an indicator to detect the degree of chemical reactionscaused by ultrasonic irradiation (JP Patent Publication (kokai) No.H04-332541 A (1992)).

SUMMARY OF THE INVENTION

Ultrasonic phantoms that had been used in the past involved the use ofsecondary actions such as temperature change or chemical reactionsresulting from ultrasonic irradiation. In general, such secondaryactions required an irradiation time of 1 to several seconds. Thus,application thereof was difficult for short ultrasonic pulses. Sincedetection was performed upon protein denaturation or chemical reactions,what could be determined based thereon was whether or not the ultrasonicirradiation exceeded a given dose. When a temperature change was to bedetected based on protein denaturation, for example, what could bedetermined was whether or not a temperature was not higher than or notlower than a temperature at which a protein could be denatured withinseveral seconds (i.e., about 70° C.). Even if the application of anadequate or greater dose of ultrasound beams was detected at theaffected area, accordingly, it was difficult to detect the dose ofultrasonic irradiation at areas other than the affected area; i.e., itwas difficult to determine whether or not the dose of ultrasonicirradiation at such areas was sufficiently small. When the oxidizationreaction caused by a substance having a high oxidizing power was used,radicals are involved in the reaction, which exist even after theultrasound exposure and, the remaining radicals proceed reaction andterminate only when reaction substrates are all consumed. Accordingly,the quantities of radicals initially generated by ultrasonic irradiationwould not affect the final reaction yield at more than 10 minutes afterthe ultrasonic irradiation. If ultrasound beams were applied with variedintensity, what could be learned therefrom was qualitative informationconcerning the generation of radicals, and it was difficult to attainquantitative information concerning ultrasonic intensity.

The present invention is intended to provide an ultrasonic phantom thatcauses optical changes upon ultrasonic irradiation of a given intensityor higher. It can be applied to shorter pulses and can arbitrarilychange ultrasonic intensity, which causes optical changes.

The ultrasonic phantom according to the present invention is composed ofa bubble-forming component comprising volatile liquid droplets and amatrix comprising the bubble-forming component uniformly dispersedtherein. The droplets contained in the ultrasonic phantom of the presentinvention may comprise therein such volatile liquid and, as the outerenvelope, a surfactant and a droplet stabilizer. Alternatively, theultrasonic phantom of the present invention may be composed of abubble-forming component comprising volatile liquid droplets, anindicator of temperature increase that irreversibly causes opticalchanges upon temperature increase, and a matrix that comprises thebubble-forming component and the indicator of temperature increaseuniformly dispersed therein.

Specifically, the present invention provides a phantom comprising: athermally-irreversible gel; a contrast medium accommodated in the gelthat causes a shift from a liquid phase to a gas phase upon ultrasonicirradiation; and a container that accommodates thethermally-irreversible gel and the contrast medium.

In one embodiment, the contrast medium comprises volatile liquid. Whenthe volatile liquid is in a liquid phase, the contrast medium comprisesfirst droplets having an average particle diameter of 0.5 μm or smallerand second droplets having an average particle diameter greater than 0.5μm and 20 μm or less. Preferably, the second droplets account for 50% ormore of the contrast medium by weight.

The thermally-irreversible gel is composed of a first area, whichincludes the focal point of the ultrasonic irradiation, and a secondarea, which does not include such focal point. In the first area, thesecond droplets account for 50% or more of the contrast medium byweight. In the second area, the second droplets account for 0% to 10% ofthe contrast medium by weight.

According to a given embodiment, the contrast medium comprises an outerenvelope comprising a surfactant and a droplet stabilizer. Also, thecontrast medium may shift from a gas phase to a liquid phase uponcooling after ultrasonic irradiation.

Examples of the volatile liquid include fluorotrichloromethane,dibrodifluoromethane, 2-bromo-1,1,1-trifluoroethane, 2-methylbutane,perfluoropentane, 1-pentene, pentane, 2H,3H-perfluoropentane,perfluorohexane, hexane, 1H-perfluorohexane, perfluoroheptane, heptane,and perfluorooctane.

The phantom of the present invention may further comprise an indicatorof temperature increase accommodated in the thermally-irreversible gel.In one embodiment, the indicator of temperature increase is a protein.

The present invention also provides a method for assaying ultrasonicirradiation conditions comprising the steps of:

applying ultrasound beams to a phantom comprising athermally-irreversible gel, an indicator of temperature increaseaccommodated in the gel, and a contrast medium that shifts from a liquidphase to a gas phase upon ultrasonic irradiation and shifts from a gasphase to a liquid phase upon cooling after ultrasonic irradiation;

attaining first detection results by optically detecting denaturation ofthe indicator of temperature increase resulting from ultrasonicirradiation and a shift of the contrast medium from a liquid phase to agas phase;

cooling the phantom following the step of ultrasonic irradiation;

attaining second detection results by optically detecting a shift of thecontrast medium from a gas phase to a liquid phase following the step ofcooling; and

comparing phase shifts of the contrast medium based on the first and thesecond detection results to assay the ultrasonic irradiation conditionsbased on the results of comparison. In the step of cooling, for example,the phantom is cooled to −20° C. to 10° C.

EFFECTS OF THE INVENTION

The ultrasonic phantom of the present invention can respond toultrasonic beams of short pulses to ultrasonic beams of continuous wavesand can respond to ultrasound beams of different intensities forvisualization of the intensity of the applied ultrasound beams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of particle diameter distribution of dropletsused for the ultrasonic phantom of the present invention.

FIG. 2 shows an example of an optical image obtained after sealing thedroplets used for the ultrasonic phantom of the present invention in thegel and applying convergent ultrasound beams thereto.

FIG. 3 shows an example of the results of assaying the ultrasonicintensity threshold that causes the gel to optically change when theparticle diameters of the droplets in the gel used for the ultrasonicphantom of the present invention are varied.

FIG. 4 shows an example of the results of assaying the ultrasonicintensity threshold that causes the gel to optically change when largedroplets (particle diameter: 1 μm) are mixed with small droplets(particle diameter: 0.2 μm) at different percentages and sealed in thegel used for the ultrasonic phantom of the present invention.

FIG. 5 shows the phantom immediately after ultrasonic application andlow-temperature treatment of the gel used for the ultrasonic phantom ofthe present invention.

FIG. 6 shows an outer frame of the ultrasonic phantom according to anexample of the present invention.

FIG. 7 shows a gel, which is the ultrasonic phantom body according to anexample of the present invention.

FIG. 8 shows an outer frame of the ultrasonic phantom according to anexample of the present invention.

FIG. 9 shows a gel, which is the ultrasonic phantom body according to anexample of the present invention.

FIG. 10 shows an example of an apparatus used in combination with theultrasonic phantom of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In conventional ultrasonic phantoms, the principal how theultrasound-exposed area is visualized disables quantitativevisualization of the differences in acoustic properties such as acousticintensity. In the case of a phantom that allows visualization ofaggregation resulting from protein denaturation, the temperature atwhich a water-soluble protein is aggregated within several seconds isbetween approximately 60° C. and 70° C., and the degree of proteinaggregation is insufficient at temperatures outside such range. Thus,such phantom is less useful. When the amount of generated substanceshaving a high oxidizing power is intended to be visualized, a radicalreaction is sequentially continued after the termination of ultrasonicirradiation until the reaction substrate is eliminated, even if theamounts of the substances generated upon ultrasonic irradiation varybecause of different conditions such as ultrasonic intensity. Thiscomplicates the visualization of variations resulting from differentultrasonic conditions.

The present inventors accordingly considered that a novel phantom havinga principle different from that of a conventional phantom would berequired in order to resolve the above-described problem and conductedstudies in this respect. The present inventors focused on opticalchanges resulting from a shift from a liquid phase to a gas phase. Whilethe liquid medium contains microparticles including liquids differentfrom the medium and the liquid molecules in the microparticles areconverted to gas, in general, volume is raised to approximately threeorders of magnitude due to differences between the density of asubstance in the liquid state and gas state that corresponds thereto.Since nanoparticles can be substantially spherical, the volume would beproportional to the diameter raised to the third power. When volume israised to approximately the third power, accordingly, the diameters ofthe microparticle grow an order of magnitude. The scattering cross area,which is an indicator of the scattering intensity, is proportional tothe radius raised to the second power. If the liquid-containingmicroparticles are shifted to a gas phase via ultrasonic irradiation,accordingly, an increased scattering cross area would enablevisualization of the areas that have been irradiated selectively withultrasound beams. The present inventors discovered that superheatingwould be suitable for shifting a liquid phase to a gas phase viaultrasonic irradiation. As demonstrated by the Kelvin's equation:log(p _(—) r/p)=−2γM/ρrRTwherein p represents vapor pressure at a horizontal surface; p_rrepresents vapor pressure of a microparticle having a radius r; Mrepresents molar mass; γ represents surface tension; ρ representsconcentration of liquid; and T represents the absolute temperature, thevapor pressure of liquid becomes smaller as the radius thereof isdecreased in the state of a microparticle. Thus, an apparent boilingpoint is increased as the radius is decreased. However, the vaporpressure is returned to a general state if an increased apparent boilingpoint is disturbed by external energy. With the utilization thereof,volatile liquid can be converted to droplets using a surfactant at atemperature sufficiently lower than the boiling point, and droplets canbe bubbled via ultrasonic irradiation at around the boiling temperatureor at higher temperatures. By causing such bubbling in a highlytransparent medium containing droplets sealed therein, the targetultrasonic phantom can be obtained.

Specifically, the ultrasonic phantom of the present invention iscomposed of a bubbling component comprising volatile liquid droplets anda matrix comprising such bubbling components uniformly dispersedtherein. The volatile liquid contained in the bubbling component of theultrasonic phantom of the present invention is preferably maintained inthe matrix while stabilizing droplets. Table 1 shows examples ofvolatile liquids preferable as bubbling components. The dropletscontained in the ultrasonic phantom of the present invention comprisethe volatile liquid and, as an outer envelope, a surfactant and adroplet stabilizer. Types of surfactants are not particularly limited,and a low-molecular-weight or high-molecular-weight and anionic,cationic, or nonionic surfactant, a phospholipid, or a protein can beused. The matrix of the ultrasonic phantom of the present invention isnot particularly limited, provided that the droplets can be spatiallyuniformly disposed. A liquid or solid matrix may be used. As a liquidmatrix, a highly viscous polyhydric alcohol is preferable. Also, a gelcan be used as the matrix of the ultrasonic phantom of the presentinvention. Gel is classified into a thermally-reversible gel thatrequires a temperature-changing operation such as heating or cooling atthe time of preparation and a thermally-irreversible gel. In the presentinvention, a gel comprises volatile liquid droplets. Thus, the latterthermally-irreversible gel is more preferable. TABLE 1 Volatile liquidBoiling point (° C.) Fluorotrichloromethane 24 Dibrodifluoromethane 252-bromo-1,1,1-trifluoroethane 26 2-methylbutane 27.8 Perfluoropentane29.5 1-pentene 30 Pentane 36 2H,3H-perfluoropentane 53.6 Perfluorohexane56.6 Hexane 69 1H-perfluorohexane 70 Perfluoroheptane 82.5 Heptane 98.3Perfluorooctane 105

The present inventors discovered the following. The droplets sealed inthe thermally-irreversible gel (i.e., a contrast medium) are subjectedto phase-shift via ultrasonic irradiation to generate bubbles, thebubbles are cooled, and the generated bubbles are reconverted todroplets. Based on this finding, the present inventors have developed anultrasonic phantom, which is a dosemeter that measures the appliedultrasonic intensity and that can measure temperature increase resultingfrom ultrasonic irradiation, and they considered that dose measurementsusing the same would be feasible. The matrix can also comprise anindicator of temperature increase that causes irreversible opticalchanges upon temperature increase. Thus, the distributional conditionsof doses and the distributional conditions of temperature change can becompared based on phantom measurements before and after temperaturechanges. The ultrasonic phantom for measuring the ultrasonic intensityand temperature increase caused by ultrasonic application may becomposed of a bubbling component comprising volatile liquid droplets, anindicator of temperature increase that causes irreversible opticalchange due to temperature increase, and a matrix that comprises thebubbling component and the indicator of temperature increase uniformlydispersed therein. The indicator of temperature increase that causesirreversible optical change due to temperature increase is notparticularly limited, as long as it is uniformly miscible with thebubbling component and the matrix. A protein that is whitened uponthermal denaturation is preferable. Specifically, a solution containinga large quantity of proteins such as albumin, egg albumen, or bloodserum (from which a given protein may or may not be separated) can beused.

EXAMPLES

Hereafter, test examples and examples of the present invention aredescribed in greater detail, although the technical scope of the presentinvention is not limited thereto.

Droplets comprising a phospholipid as the outer envelope and comprisingperfluorocarbon were incorporated into a polyacrylamide gel, andultrasound beams were applied thereto. Changes resulting therefrom weretested. Droplets comprising perfluorocarbons and substances of similarproperties are referred to as contrast media herein. In advance, aphantom as a test sample was prepared in the following manner.

(Preparation of Droplets)

The ingredients shown below were added together while being maintainedat 4° C., and the resulting mixture was homogenized using theUltra-Turrax T25 (Janke & Kunkel, Staufen, Germany) at 9,500 rpm atfreezing temperature for 1 minute while slowly adding 20 ml of phosphatebuffer (pH=7.4) thereto. Glycerol 2.0 g α-Tocopherol 0.02 g  Cholesterol0.1 g Lecithin 1.0 g Perfluoropentane 0.2 g

The resulting emulsion was subjected to high-pressure emulsification inthe Emulsiflex-C5 (Avestin, Ottawa, Canada) at 20 MPa for 1 minute, andthe resultant was filtered through a 5-μm membrane filter. Further, thefiltrate was centrifuged at 5,000 G for 5 minutes, the supernatant wasremoved, phosphate buffer (pH=7.4) in an amount equivalent to the amountof the removed supernatant was added, and the resultant was subjected toredispersion using a vortex mixer for 30 seconds. The particle diameterdistribution of the resulting emulsion droplets was assayed using LB-550(Horiba Seisakusho, Tokyo, Japan). Examples of the results are shown inFIG. 1. Emulsion droplets having an average particle diameter of 1.18 μmwere obtained. The pore size of the membrane filter to be used, thegravity and the duration of centrifugation, and the numbers of times offiltering and of centrifugation can be changed to obtain emulsiondroplets having average particle diameters of about 0.1 μm to about 5μm. Alternatively, the aforementioned high-pressure emulsification wasperformed at 0.1 MPa (atmospheric pressure) instead of 20 MPa, andemulsion droplets having average particle diameters of about 5 μm toabout 20 μm were obtained. The concentration of perfluoropentanecontained in the emulsion droplets was assayed using a gas chromatographG-6000 (Hitachi High-Technologies, Ibaraki, Japan; column: Gaskuropack54 80/100). Instead of lecithin, sodium dodecyl sulfate and Triton X100were used, and emulsion droplets having substantially equivalentparticle diameter were obtained.

(Sealing of Droplets into Gel)

(1) Preparation of Gel that Does Not Contain an Indicator of TemperatureIncrease

All the following procedures were performed at 4° C. The emulsion (5 ml)containing the droplets with an average particle diameter of 1.18 μm(perfluoropentane concentration: 10 mM), 86.5 ml of water, and 25 ml ofa 40% acrylamide solution (acrylamide:bisacrylamide=39:1) werethoroughly mixed and poured into a rectangular container. While slowlyagitating the solution with a stirrer, 7.5 ml of a 10% ammoniumpersulfate solution and 10 ml of N,N,N′,N′-tetramethylethylenediaminewere quickly added and homogeneously mixed. Upon termination ofagitation, the stirrer rod was removed, the rectangular container wascovered, and the container was allowed to stand for 20 minutes. Thus, asubstantially transparent gel was prepared.

(2) Preparation of Gel that Contains an Indicator of TemperatureIncrease

All the following procedures were performed at 4° C. The emulsion (5 ml)containing the droplets of the average particle diameter of 1.18 μm(perfluoropentane concentration: 10 mM), 86.5 ml of a 5% bovine serumalbumin solution, and 25 ml of a 40% acrylamide solution(acrylamide:bisacrylamide=39:1) were thoroughly mixed, and the mixturewas poured into a rectangular container. While slowly agitating thesolution with a stirrer, 7.5 ml of a 10% ammonium persulfate solutionand 10 ml of N,N,N′,N′-tetramethylethylenediamine were quickly added andhomogeneously mixed. Upon termination of agitation, the stirrer rod wasremoved, the rectangular container was covered, and the container wasallowed to stand for 20 minutes. Thus, a substantially transparent gelwas prepared.

Test Example 1 Effects of Ultrasonic Irradiation with Different AcousticIntensity

The gel prepared in accordance with the method described in (1) abovewas maintained at 37° C., the gel was brought into close contact with aconverging ultrasonic transducer having a diameter of 24 mm and an Fnumber of 1 in such state, the acoustic intensity was varied from 0 to300 W/cm², and the gel was irradiated with 4 periods of 4 MHz ultrasoundbeams. An overview of the gel is shown in FIG. 2. FIG. 2 is a binarypicture obtained by placing the gel irradiated with ultrasound beams ona black plate, photographing the gel, and binarizing the photograph viaimage processing. When the acoustic intensity was 0 (without ultrasonicirradiation), the gel remained black. This indicates that the gel issubstantially optically transparent. When the gel was irradiated withultrasound beams, however, the areas around the focal point werewhitened. The whitened areas became larger as the ultrasonic intensitybecame higher. This demonstrates that the gel used in this test exampleis whitened at a site that has been irradiated with ultrasound beams ofa given intensity or higher (an acoustic intensity of 50 W/cm² in thecase of FIG. 2). Substantially the same effects were attained when theduration of ultrasonic irradiation was changed from 4 periods to 10seconds (equivalent to about 4×10⁷ periods). Also, substantially thesame results were attained using the gel prepared in accordance with themethod described in (2) above.

Test Example 2 Test of Changes in Sensitivity to Ultrasound Beams WhenDroplet Sizes are Changed

As described above, droplet sizes can be varied in accordance withconditions for preparing droplets. FIG. 3 shows an example of theresults of inspecting the ultrasonic intensity dependence resulting fromchanges in the gel shown in FIG. 2 when droplets having differentaverage particle diameters are sealed in the gel. The conditions forultrasonic irradiation were the same as in Test Example 1. Thehorizontal axis of FIG. 3 logarithmically represents an average particlediameter, and the vertical axis represents the minimal ultrasonicintensity (the ultrasonic intensity threshold) resulting from changes inthe gel shown in FIG. 2. When the average particle diameter was 0.5 μmor smaller, the ultrasonic intensity threshold was as high as about 130to 160 W/cm². When the average diameter was greater than 0.5 μm, therewas substantially no particle diameter dependence, and the ultrasonicintensity threshold was about 40 W/cm². This demonstrates that thesensitivity to ultrasound beams can be varied depending on whether ornot the particle diameter of the gel used in this test is smaller thanor greater than 0.5 μm (substantially the same results were attainedusing the gel prepared in accordance with the method described in (2)above).

Test Example 3 Test of Sensitivity to Ultrasound Beams When MixingDroplets Having Different Particle Diameters

As the particle diameters vary, sensitivity to ultrasound beams alsochanges as shown in FIG. 3, and such change is rapid relative toparticle diameters. In order to precisely alter sensitivity toultrasound beams, small droplets with low sensitivity to ultrasoundbeams (e.g., with particle diameters of 0.2 μm) were mixed with largedroplets having larger particle diameters (e.g., particle diameters of 1μm) and higher sensitivity to ultrasound beams than the small dropletsat different percentages to prepare droplet groups, and ultrasonicintensity thresholds were determined in the same experimental systemsthat were used in Test Examples 1 and 2 in the same manner as in TestExample 2, except for the use of the prepared droplet groups. FIG. 4shows an example of the determined results. The horizontal axis of FIG.4 represents the percentage of large particles out of all droplets andthe vertical axis represents the ultrasonic intensity at which the gelcomprising the droplets sealed therein changes as shown in FIG. 2. Thisfigure indicates that the ultrasonic intensity thresholds vary dependingon the percentage of large particles and that the thresholds becomelower as the percentage of large particles is increased, when the largeparticles account for 0% to 50% of all droplets by weight. Such changesare sufficiently mild relative to changes in percentage, and adjustmentof the percentage enables precise regulation of the sensitivity of thegel to ultrasound beams. Similar effects were attained in an experimentthat was carried out by varying the sizes of large droplets in the rangebetween 0.7 μm and 20 μm. Similar results were also attained when thesizes of small droplets were varied in the range between 0.1 μm and 0.5μm. Also, perfluoropentane in the droplets was substituted withperfluorohexane or perfluoroheptane, a similar experiment was carriedout, and substantially the same results were attained. Furthermore,substantially the same results were attained using the gel prepared inaccordance with the method described in (2) above.

This test example demonstrates that the gel of the present inventionthat comprises droplets sealed therein has regulated sensitivity toultrasound beams, and optical changes would occur with the applicationof ultrasound beams at a given intensity or higher.

Test Example 4 Test Example Regarding a Step of Obtaining InformationConcerning Ultrasonic Intensity Using gel Containing an Indicator ofTemperature Increase and Information Concerning Temperature Increase

The gel prepared in accordance with the method described in (2) abovewas maintained at 37° C., the gel was brought into close contact with aconverging ultrasonic transducer having a diameter of 24 mm and an Fnumber of 1 in such state, 4 MHz ultrasound beams with acousticintensity of 300 W/cm² were applied for 1 ms or 2 s, and the gel wascooled to 4° C. immediately thereafter. The temperature was maintainedat 4° C. for 1 hour and returned to room temperature, and an overview ofthe gel is shown in FIG. 5. FIG. 5 is a binary picture obtained byplacing the gel irradiated with ultrasound beams on a black plate,photographing the gel, and binarizing the photograph via imageprocessing. Regardless of the duration of ultrasonic irradiation, thefocal area was whitened immediately after ultrasonic irradiation. Whenthe duration of ultrasonic irradiation was 2 s, the site irradiated withultrasound beams remained white even when it was treated at 4° C. Thisindicates that the temperature reached the protein denaturationtemperature (about 65° C.) via ultrasonic irradiation. When the durationof ultrasonic irradiation was 1 ms, however, whitening observedimmediately after irradiation substantially disappeared via treatment at4° C. This indicates that the temperature was not increased. Thus,information concerning ultrasonic intensity and information concerningtemperature increase can be obtained via optical observation of theultrasonic phantom of the present invention immediately after ultrasonicirradiation and via further optical observation thereof after cooling tolower temperatures. Separately, another experiment was carried out byvarying the temperature of the low-temperature treatment to −20° C. to10° C. and varying the duration of treatment from 10 minutes to 3 hours.Substantially the same results were obtained.

Example 1 Example of Phantom Containing a Gel with Differing Sensitivityto Ultrasound Beams at, in Front of, and Behind the Focal Area ofUltrasonic Irradiation

Hereafter, an example of the present invention is described withreference to FIG. 6 and FIG. 7. FIG. 6 shows an outer frame of thephantom. The outer frame of the phantom comprises an outer frame body 1,an acoustic window 2 for ultrasonic irradiation, a window 3 forobserving the results of ultrasonic irradiation, and a preventive layer4 for ultrasonic reflection. FIG. 7 shows an acrylamide gel comprisingdroplets sealed therein, which is a phantom body. The phantom bodycomprises a gel 5 for the front of the focal area, a gel 6 for the focalarea, and a gel 7 for the back of the focal area. At the time of use,gels 5, 6, and 7 are first prepared, the gels are mounted on the outerframe shown in FIG. 6, and the phantom is sealed with a lid that is notshown. When used as a phantom, an ultrasonic source for assaying thedose is brought into close contact with the acoustic window 2 forultrasonic irradiation to apply ultrasound beams, and the results areobserved through the window 3 for observing the results of ultrasonicirradiation. When the ultrasonic source cannot be brought into closecontact with the acoustic window 2 for ultrasonic irradiation, thephantom and the ultrasonic source can be placed into a tank so as toapply ultrasound beams to the phantom. Alternatively, a space betweenthe acoustic window 2 for ultrasonic irradiation and the ultrasonicsource may be filled with an acoustic coupling agent such as acousticjelly to irradiate the phantom with ultrasound beams. As an embodimentof the present example, the focal area of the ultrasonic source (i.e.,an area including a focal point of ultrasonic irradiation) is irradiatedwith ultrasound beams with higher intensity than the ultrasound beams ofinterest, and the areas in front of and behind the focal area areirradiated with ultrasound beams with lower intensity than theultrasound beams of interest. In order to confirm such irradiation, forexample, a gel 5 for the front of the focal area and a gel 7 for theback of the focal area may each comprise large droplets of Test Example3 in amounts of 50% or more by weight. The gel 6 for the focal area maycomprise large droplets of Test Example 3 in amounts of 0% to 10% byweight. Use of such gels enables inspection of whether the ultrasonicintensity is approximately 100 W/cm² or higher at the focal area and ofwhether it is lower than 40 W/cm² at areas in front of and behind thefocal area.

Example 2 Example of Phantom for Estimating the Ultrasonic Intensity atthe Focal Area of Ultrasonic Irradiation

Hereafter, an example of the present invention is described withreference to FIG. 8 and FIG. 9. FIG. 8 shows an outer frame of thephantom. The outer frame of the phantom comprises an outer frame body 1,and a window 2 for ultrasonic irradiation. FIG. 9 shows a gel comprisingdroplets sealed therein, which is a phantom body. The gel is a laminateof gels 8-1 to 2 n with different sensitivities to ultrasound beams. Atthe time of use, the gel shown in FIG. 9 is mounted on the outer frameshown in FIG. 8, and the phantom is sealed with a lid that is not shown.When used as a phantom, the ultrasonic source, which is the target ofmeasurement, is brought into close contact with the acoustic window 2for ultrasonic irradiation, and the ultrasonic source is moved whilesequentially applying ultrasound beams to gel in the descending order ofsensitivity to ultrasound beams. In order to modify the sensitivity toultrasound beams, gels comprising large droplets and small droplets atdifferent percentages should be prepared as demonstrated in Test Example4.

Example 3 Example of Apparatus for Obtaining Information ConcerningUltrasonic Intensity and Temperature Increase Used in Combination withUltrasonic Phantom

Hereafter, an example of the present invention is described withreference to FIG. 10. The apparatus used in combination with theultrasonic phantom in the present example comprises a phantom holdingportion 9, a temperature regulating portion 10, a temperaturecontrolling portion 11, a phantom photographing portion 12, an apparatuscontrolling portion 13, and a display 14. The phantom holding portion 9holds a phantom as shown in FIG. 7 or 9 and it can apply ultrasoundbeams. The temperature regulating portion 10 is constructed so as toregulate the temperature of the phantom placed in the phantom holdingportion 9 in a temperature range between −10° C. and 40° C., and it iscontrolled by the temperature controlling portion 11. The phantomphotographing portion 12 is constructed so as to photograph the entirephantom, and the results of photographing are transferred to theapparatus controlling portion 13. The apparatus controlling portion 13is constructed so as to control the temperature controlling portion 11and the phantom photographing portion 12, to retain the phantom imagephotographed by the phantom photographing portion 12, and to performimage processing such as binarization or superposition. The display 14is constructed so as to display a phantom image. The apparatuscontrolling portion 13 is constructed so as to determine the temperatureat the time of ultrasonic irradiation and the temperature and theduration of low-temperature treatment upon user input. The controllingportion 13 transmits a control signal to the phantom photographingportion 12 after ultrasonic irradiation and low-temperature treatment tocommand the initiation of photographing.

INDUSTRIAL APPLICABILITY

The ultrasonic phantom of the present invention can respond toultrasonic beams of short pulses to ultrasonic beams of continuous wavesand allows visualization of the ultrasonic intensity applied in responseto different ultrasonic intensities. The present invention is useful invarious diagnostic and therapeutic techniques in the medical field.

1. A phantom comprising: a thermally-irreversible gel; a contrast mediumaccommodated in the gel that causes a shift from a liquid phase to a gasphase upon ultrasonic irradiation; and a container that accommodates thethermally-irreversible gel and the contrast medium.
 2. The phantomaccording to claim 1, wherein the contrast medium comprises volatileliquid, and when the volatile liquid is in a liquid phase, the contrastmedium comprises first droplets having an average particle diameter of0.5 μm or smaller and second droplets having an average particlediameter greater than 0.5 μm and 20 μm or less.
 3. The phantom accordingto claim 1, wherein the second droplets account for 50% or more of thecontrast medium by weight.
 4. The phantom according to claim 1, whereinthe thermally-irreversible gel is composed of a first area, whichincludes the focal point of the ultrasonic irradiation, and a secondarea, which does not include such focal point, and in the first area,the second droplets account for 50% or more of the contrast medium byweight.
 5. The phantom according to claim 1, wherein thethermally-irreversible gel is composed of a first area, which includesthe focal point of the ultrasonic irradiation, and a second area, whichdoes not include such focal point, and in the second area, the seconddroplets account for 0% to 10% of the contrast medium by weight.
 6. Thephantom according to claim 1, wherein the contrast medium comprises anouter envelope comprising a surfactant and a droplet stabilizer.
 7. Thephantom according to claim 1, wherein the volatile liquid is any memberselected from among the group consisting of fluorotrichloromethane,dibrodifluoromethane, 2-bromo-1,1,1-trifluoroethane, 2-methylbutane,perfluoropentane, 1-pentene, pentane, 2H,3H-perfluoropentane,perfluorohexane, hexane, 1H-perfluorohexane, perfluoroheptane, heptane,and perfluorooctane.
 8. The phantom according to claim 1, which furthercomprises an indicator of temperature increase accommodated in thethermally-irreversible gel.
 9. The phantom according to claim 8, whereinthe indicator of temperature increase comprises proteins.
 10. Thephantom according to claim 1, wherein the contrast medium shifts from agas phase to a liquid phase upon cooling after ultrasonic irradiation.11. A method for assaying ultrasonic irradiation conditions comprisingthe steps of: applying ultrasound beams to a phantom comprising athermally-irreversible gel, an indicator of temperature increaseaccommodated in the gel, and a contrast medium that shifts from a liquidphase to a gas phase upon ultrasonic irradiation and shifts from a gasphase to a liquid phase upon cooling after ultrasonic irradiation;attaining first detection results by optically detecting denaturation ofthe indicator of temperature increase resulting from ultrasonicirradiation and a shift of the contrast medium from a liquid phase to agas phase; cooling the phantom following the step of ultrasonicirradiation; attaining second detection results by optically detecting ashift of the contrast medium from a gas phase to a liquid phasefollowing the step of cooling; and comparing phase shifts of thecontrast medium based on the first and the second detection results toassay the ultrasonic irradiation conditions based on the results ofcomparison.
 12. The method for assaying ultrasonic irradiationconditions according to claim 11, wherein the step of cooling comprisescooling the phantom to −20° C. to 10° C.